In this continuation of the article "Archiving in SCADA and MES systems" we will show the advantages of the structured archives and the ability to archive the future :-).
Let's get back to statistical or calculated archives. Experience has shown that the same calculation is often used for different data (e.g. the hourly consumption is calculated for each of several dozen machines). In this case, it is quite tedious to configure the same thing many times, just with different source objects. Not to mention how to prevent errors or typos, or reconfigure all such archives in the event of a change.
Is there any way we can make the work of the configurator easier? D2000 supports work with so-called structured variables (abbreviated as structures). A structure is a table with N rows, whose columns have a specific type (analog, integer, text, boolean, or object reference). We are interested in columns of the object reference type, which allow you to "connect" for example, a measured or calculated point, to a specific position in the table.
The D2000 Archive can archive both the column of a structure and the entire structure as the primary archive. If objects are connected in the structure, their values are archived. So by configuring one archive, it is possible to archive multiple objects - all with the same parameters (time depth, type of archiving, and more).
At the same time, if a user or a script wants to retrieve historical values of an object (e.g. measured point), the D2000 Server automatically detects that the object is connected in a structure that is archived and requests values for the respective row and column of the structure in which this specific object is connected from the D2000 Archive.
Similarly, statistical and computed archives can be structured (work with structured source archives). In Figure 2 it is possible to notice the syntax of the structured computed archive - the syntax H.Name[0] speaks of the whole column of the structured archive H.Name (a specific row would be referenced e.g. H.Name[3]).
Thus, by connecting D2000 objects to structures and then configuring structured archive objects, it is possible to significantly speed up and clarify the configuration of archives in applications with repetitive technology.
Another advantage is when adding new devices. After handling communication (creation of measured points) it is enough to add new rows to the structures and connect new measured points to them. There is no need to change the configuration of the archive - after detecting that the structures have been enhanced, it will automatically start working with new rows as well!
In the past, computed archives and structured archives were only available for the more powerful enterprise version of the D2000 called Entis and were not available in the basic version called D2000 Actis. As of version 9.1 (December 2012), which unified the versions, this limitation has been removed and this functionality is available to all configurators.
Archive objects can be active – they can publish their value. The value of the archive object is the latest archived value with the corresponding timestamp. In the case of calculated and statistical archives, it is thus possible to display the value of the archive directly in the scheme to the user (similar to, for example, the calculated point). In the case of structured archives, it is possible to define a structure or a column of the structure in which the values of the items of the structured archive are published.
And finally, one more interesting feature. The archive is usually used to archive historical data, right? But in D2000 systems, we can also archive the future. However, not real, only planned :-) . There is nothing to prevent values being inserted into the archive from the script to have timestamps from the future. There is nothing special about it yet. However - if such an archive is configured to publish its value and is also periodic - it can be configured to "replay" in real-time the values that have been pre-stored by the script. The feature is useful, for example, in implementing a plan-to-reality comparison view, which means that the user can then view the planned and actual production side by side in the schema, with the planned production "living" and changing periodically according to data prepared and stored in the archive.
The described configuration options of the D2000 Archive enable efficient and convenient work of the configurator when developing or enhancing the SCADA and MES applications. Maintaining the consistency of statistical and calculated archives after entering the old values, as well as the ability to manually control calculations allow the deployment of D2000 in applications performing continuous as well as on-demand balancing. Structured archives simplify and clarify the configuration of repetitive technological units, machines, etc.
In a separate article, we will focus on the enterprise features of D2000 Archive in terms of long-term data archiving, supported SQL databases, parallelisms and other features that are used by multiple applications with tens of thousands of archive objects, archive databases with hundreds of GB and data flow of hundreds to thousands of values archived every second.
Ing. Peter Humaj, www.ipesoft.com
